The follow-up of the cohort of multiple sclerosis (MS) patients will be continued for the seventh year of the study. Analysis of the mortality and other data will continue. The data collected in the third-year of the longitudinal study of humoral and cell-mediated immunity in cohabitant controls and MS patients with progressive or relapsing courses will be further analyzed. Data collection and analysis of the study of genetic and environmental factors in families with more than one case of MS will be completed. Data collection for the case-control study of MS patients and siblings matched for genetic susceptibility to MS will be completed. Further analysis of all aspects of these studies will be carried out. The study of the apparent time-space cluster in 1954-55 in King County has been terminated, since additional case-finding efforts resulted in a lessening of the differences in rates.